1. Scope of the Invention
The present invention relates generally to processes for making stable poly(hydrido siloxane) inorganic polymers and methods of manufacturing films thereof, and more specifically to stable poly(hydrido siloxane) polymers for use as dielectric films and methods of manufacture thereof.
2. Related Art
Advances in the semiconductor industry are characterized by the introduction of new generations of integrated circuits (IC's) having higher performance and greater functionality than that of the previous generation. These advances are often the result of reducing the size of the IC devices. However, as device geometries become smaller, the dielectric constant of an insulating material used between conductive paths, for example, silicon oxide (SiO.sub.2), becomes an increasingly important factor in device performance. Reducing this value below the approximately 3.9 of a SiO.sub.2 film advantageously lowers power consumption, reduces crosstalk, and shortens signal delay for closely spaced conductors.
Often, fabricating IC devices requires creating multilevel interconnect structures. One challenge in implementing multilevel interconnect structures for IC devices and particularly for submicron IC devices is to planarize multilevel metal structures. Spin-on glass (SOG) materials have been widely used to create dielectric films to planarize such structures.
The commonly used SOG materials are generally characterized either as SOG's having organic substituents, termed organic SOG's, or SOG's without such substituents termed inorganic SOG's. Films made from organic SOG's provide good planarization. However, when such materials remain over locations where vias, or contact openings, are to be made, a common problem known as "poisoned-vias" is often encountered. To avoid the poisoned-via problem, an additional process step, known as an etchback step is generally employed to remove SOG material from via locations.
Dielectric films made from previously known inorganic SOG's avoid the poisoned-via problem without an etchback step. However, such films have other problems. First, generally the previously known inorganic SOG films exhibit higher dielectric constants than organic SOG films. Additionally, films made of these inorganic SOG's having sufficient thickness for use as interlevel dielectric layers are susceptible to cracking. Thus it would be desirable to have an inorganic SOG that forms crack resistant films having a low dielectric constant.
Films based on the cage structure hydrogen silsesquioxane (HSQ) resin, for example, as described in U.S. Pat. No. 4,756,977, "MULTILAYER CERAMICS FROM HYDROGEN SILSESQUIOXANE," are one attempt at achieving the aforementioned goals. Films produced from such HSQ resins are known to have dielectric constants as low as 3.0 and can be made as thick as 1 .mu.m with little or no cracking. However, HSQ resins having a cage structure form films that include strained Si-O bonds which are reactive toward alcohols, acetone, and esters. The cage HSQ resin is known to gel quickly in acetone or ethyl acetate solvents. Cage HSQ resins also have a substantially ordered structure which requires melting and reflow to achieve planarization. In addition, films produced from cage HSQ resins are reported to degrade upon exposure to an oxygen plasma. The unstable nature of films formed using cage structure HSQ resins is overcome by alternate HSQ materials, for example branched polymers. Branched HSQ polymers with silanol end groups are more stable in solutions of alcohols, acetone and ethyl acetate than cage HSQ resins. However, branched HSQ polymers in solution, increase in molecular weight over time due to polymer cross-linking. A stable HSQ polymer material having a branched, or ladder, structure is described in Japanese Kokai Patent No. Sho 60-12493. However, the polymer material in Sho 60-12493 is terminated with trialkylsiloxy groups. Hence films formed therefrom are susceptible to degradation by an oxygen plasma.
Thus it would be desirable to manufacture and use an inorganic SOG material that is resistant to degradation by commonly used oxygen plasmas. It would be desirable for the SOG material to allow for the formation of films that are amorphous in character. It would also be desirable for such SOG material to be stable when stored for longer than 3 months. In addition, it would be desirable for films formed from the SOG material to exhibit good gap filling characteristics and to have good adhesion to a variety of semiconductor materials. It would further be desirable for films formed from the inorganic SOG to have good thermal stability as evidenced by low water absorption and to be formulated with common solvents.